This invention relates to hybrid switching circuits and in particular to novel switching techniques and apparatus that permit high power switching with intermediate power level switching means.
Many electronic systems require the switching of high current carrying lines with bw or intermediate power switching devices. A particular example of this, and one in which the present invention finds great utility, is the control of the feeds to airborne antennas that are remotely switched between two modes of operation. Systems of this type commonly employ a pair of antennas that are fed by a switching circuit that provides either full power to one antenna (single mode operation) or half power to each antenna (double mode operation). It is usually required that such antennas transmit several kilowatts of average c.w. power over a wide frequency range while maintaining low VSWR characteristics. Conventional switching methods used to produce the "dual" or "single" mode performance have been found inadequate either because of the adverse effect of changing impedance levels on VSWR or because of the size and weight limitations of the full power switches. Although 3dB hybrid switches have been used to switch between full power to one of two feeds and one half power to each of the two feeds they also have limitations that render them less than desirable for many applications. In particular, the conventional quarter wave 3dB hybrid is restricted in power handling capability and manifests performance sensitivity to tolerance variations. Such a device also requires "touchy" tuning devices at higher frequencies. Other currently available switching means also exhibit the foregoing and other undesirable characteristics. Accordingly there currently exists the need for a high power, light weight switch suitable for airborne applications that is not subject to the above enumerated deficiencies of known switching circuits. The present invention is directed toward satisfying that need.